fix(collaboration): harden delegated task isolation (#1486)

* feat(collaboration): isolate delegated artifacts and child runs

Isolate delegated inputs and outputs behind secure artifact exchange lifecycles. Scope Agent Link tasks by tenant and root agent, and enforce delegation spawn-tree boundaries. Add process-wide child-run admission and preserve logical media paths across native, MCP, and sandbox execution.

* fix(collaboration): harden delegated task isolation

Enforce tenant and root-agent task scope across migrations and stores. Add exactly-once async completion delivery, delegated sandbox boundaries, and confined artifact and media recovery across runtime surfaces.

* fix(collaboration): recover interrupted async tasks

* fix(collaboration): normalize persisted child-run status

---------

Co-authored-by: ntduc <ntduc@cpp.ai.vn>

internal/workspace/workspace_context.go

@@ -10,9 +10,9 @@ import "context"
 type Scope string
 
 const (
-	ScopePersonal Scope = "personal"  // single user, isolated
-	ScopeTeam     Scope = "team"      // team context, shared or isolated
-	ScopeDelegate Scope = "delegate"  // delegated task, scoped access
+	ScopePersonal Scope = "personal" // single user, isolated
+	ScopeTeam     Scope = "team"     // team context, shared or isolated
+	ScopeDelegate Scope = "delegate" // delegated task, scoped access
 )
 
 // WorkspaceContext is resolved ONCE at run start, immutable for the entire run.
@@ -24,13 +24,6 @@ type WorkspaceContext struct {
 	// Scope describes the access boundary type.
 	Scope Scope
 
-	// ReadOnlyPaths are additional paths the agent can read but NOT write.
-	ReadOnlyPaths []string
-
-	// SharedPath is the shared delegate area (read/write by both delegator + delegatee).
-	// nil when not in delegation context.
-	SharedPath *string
-
 	// TeamPath is the team workspace root (nil if not in team context).
 	TeamPath *string
 
@@ -65,7 +58,6 @@ type ResolveParams struct {
 	PeerKind   string // "direct" | "group"
 	TeamID     *string
 	TeamConfig *TeamWorkspaceConfig
-	DelegateCtx *DelegateContext
 	BaseDir    string
 }
 
@@ -81,13 +73,6 @@ func (c *TeamWorkspaceConfig) IsShared() bool {
 	return c != nil && c.WorkspaceScope == "shared"
 }
 
-// DelegateContext carries delegation-specific workspace overrides.
-type DelegateContext struct {
-	LinkID      string
-	SharedPath  string
-	ExportPaths []string // read-only exports from delegator
-}
-
 // DefaultEnforcementLabel returns a human-readable workspace description
 // for system prompt injection based on scope and sharing mode.
 func DefaultEnforcementLabel(scope Scope, shared bool) string {